1. Field of the Invention
This invention relates to the testing of laminated substrates used in packaging integrated circuit dies and, in particular, to a method and apparatus for identification of defective laminated substrates.
2. Description of the Related Art
Integrated circuit chips or dies are susceptible to damage and failure when exposed to environmental conditions such as heat and moisture. To protect a die and, therefore, extend its life span, it is packaged within a protective barrier of material which contains metallic pads and leads to provide electrical connection to the die itself. The fabrication of the package may involve the creation of a substrate capable of receiving an integrated circuit die and providing electrical connections to that die. Package substrates are typically laminate structures of insulating material having a die mounting site which secures the die and contains metal lines or layers which are fashioned to electrically connect the die to leads which extend outside the package. The leads may be contacted from outside the insulating material and used to connect the packaged die to another element, for example a circuit board. Advancements in processing techniques of package substrates have allowed both laminate substrates to be almost fully processed in an array and then divided from the array into numerous individual package substrates, and for one or multiple die mounting sites to be present on a single package substrate.
The mounting of the dies within a package may be accomplished by placing the dies on a package substrate which is typically a ceramic or other insulating material combined with metal lines and/or layers to provide appropriate electrical connections. The package substrate is a laminate construction. In order to shield the dies, they are generally encased within the package by methods such as epoxy or resin encapsulation or by sealing in a container which is vacuum-sealed or filled with an inert gas.
Several different packaging technologies are currently in use for semiconductor manufacturing, including thin quad flat packs (TQFPs), ball grid arrays (BGAs), tape automated bonding (TAB), ultra-thin packages, bare chips or chip-on-board (COB), flip-chip assemblies and multichip modules (MCMs).
BGA packages, for example, are common and are generally constructed using a plastic or ceramic laminated substrate as shown in FIG. 5. The package substrate 20 is a laminate construction of a conducting (metal) patterned layer 54, electrically insulating layers 52 and 56, and conducting ball grid array 62. A die mounting site 30 is formed in the layer 52 to accept an IC die. Insulating layers 52 and 56 may be, for example, a ceramic or plastic material having vias through which an electrical connection is made between the contacts 58 of the die site 30 and the ball grid array 62 through the metal pattered layer 54. Electrical connections to the die itself are made through the contacts 58. The die is typically wire bonded to the contacts 58 within the die mounting site 30. The die is generally face up, with its back side bonded to the substrate package 20 through the wire bonds and, in some cases, through the use of an adhesive. The ball grid array 62 is comprised of a plurality of individual solder balls 64 which provide electrical contact to a circuit board or another package.
Semiconductor packages are subject to a variety of heating and depositing processes during fabrication. Accordingly, a package substrate is susceptible to defects arising from any step in the fabrication process. A defective package substrate may render a die useless even if the die itself is flawless. Testing for defects within package substrates may occur at any point in the processing prior to introduction of the die. Commonly, it is accomplished after processing of the laminate layers is complete and prior to introduction of the die. Testing may be accomplished through a variety of methods, the most common being visual inspection by a human operator and by electronic probe testing. Visual inspection is accomplished by an operator utilizing a high resolution image of the die mounting sites on the laminate substrate to detect and analyze defects. Such a process is both expensive and time-consuming. In-line testing is also accomplished through the use of electronic probes which contact the die connection points of the individual die mounting sites within the laminated substrate and check for proper operation to determine the presence or absence of defects.
Once an incapacitating defect has been found on an individual die mounting site, that die mounting site must be marked for analysis, repair, and/or destruction. Normally, this is accomplished by marking the die mounting site with a unique identification such as a print or ink media based tag. The laminated substrate may then be scored and separated into individual package substrates each having at least one die mounting site. The package substrates containing defective die mounting sites which have been marked as defective are eventually discarded or repaired. To implement this system, a code mark, such as a bar code, is applied to each individual package substrate or die mounting site prior to testing. After testing, the code mark is read and stored in a computer memory along with a designation of test results as defective or non-defective. The code mark is unique to each die mounting site and, therefore, the processing system may read the code mark at later time and redirect the defective die mounting sites to a repair station or a discard bin. However, ink-based marks or codes on the surfaces of substrates are subject to obfuscation and destruction during the laminate fabrication and/or package assembly processes.
Another identification method is to retain order within the processing system by assigning each package substrate or die mounting site a unique number in that system. If a defect is found in a die mounting site that has been assigned, for example, the number 23, the system will later skip or discard the 23rd die mounting site and associated substrate within the line. Such a process, however, requires complicated sorting and processing machinery to retain the order which has been assigned.
Automated processes for the analysis, repair, and destruction of defective package substrates are preferred in light of the possible increases in efficiency and cost reduction it makes possible. Identifying the defective package substrates is essential within such a system. Currently no method or apparatus allows for in-line identification of defective individual package substrates without the use of complicated machinery or computing resources.
The present invention provides a method and apparatus that is able to overcome some of the problems attendant the marking and subsequent analysis of defective laminate package substrates.
The above and other features and advantages of the invention are achieved by providing an apparatus for the production of at least one hole within the boundary of an individual package substrate containing at least one die mounting site prior to the mounting of integrated circuit dies to the die mounting site(s). This hole is covered with a material layer coating composed of an opaque material such as a resist. The coating may then be selectively removed at a later point during the fabrication process dependent upon whether the individual package substrate has been classified as defective or non-defective. Later equipment can read the state of the hole as covered or not to determine the status of the individual package substrate as defective or not.
After an individual substrate has been marked as defective, a light source and light collector are used in the package fabrication process arranged on opposite sides of the package substrate to determine whether the hole is blocked or not by the resist, and thus whether the individual package substrate is defective or not. Therefore, defective individual package substrates may be identified through the use of a simple light source and light collector and without the need for a manual inspection or use of complicated optical recognition equipment.
As a variant, for individual substrates employing multiple die mounting sites, it is also possible to provide a hole for each such site which is covered or not and thus be able to characterize each die mounting site on the individual package substrate as defective or not.
The above and other advantages and features of the present invention will be better understood from the following detailed description of the preferred embodiment which is provided in connection with the accompanying drawings.